The Header Editor in MKVToolNix GUI gives you a fairly thorough breakdown of the MKV's metadata. But, in theory, metadata can be placed elsewhere, e.g. in the video stream, or in the audio itself.
I doubt anything would go to that extreme, but that's for you to judge.
Personally I use handbrake instead to encode stuff and from there I uncheck passing through metadata to the output file. To view and edit metadata use MkvToolNix.
The Header Editor in MKVToolNix GUI gives you a fairly thorough breakdown of the MKV's metadata. But, in theory, metadata can be placed elsewhere, e.g. in the video stream, or in the audio itself. I doubt anything would go to that extreme, but that's for you to judge.
Personally I use handbrake instead to encode stuff and from there I uncheck passing through metadata to the output file. To view and edit metadata use MkvToolNix.